external/wayland: Uprev to 6a18a87727c64719c68168568b9ab1e4d7c2d9c1

This is the version of wayland used by chrome, which includes a
required update to the wl_touch protocol to v6.

Bug: 33457871
Test: None

Change-Id: I8fe14f1161766e5f5046181473e1d87c547eae74
34 files changed